The development of vehicle technology helps the interpersonal relationship and the living quality. Most vehicles use liquid fossil fuels such as gasoline, so it is not difficult to measure a quantity of the liquid fossil fuel used in such vehicles. But, people are becoming much more conscious and aware of the impact this has on the environment, so people are making more of an effort to reduce the dependence of petroleum. Thus, electric vehicles are much more advantaged because of their low environmental pollution, low noise, easy pollution control and various energy applications.
The electric vehicle is generally powered with a battery which is usually charged by a large current or discharges a large current, and it is not easy to accurately measure the remaining power capacity of battery. Thus, the management and analysis of battery is very important to the electric vehicle. Also, the state of charge (SOC) and state of health (SOH) of battery can be known by the variation of internal impedance and be estimated by the internal impedance variation and current temperature of a battery, where the SOC is the equivalent of a fuel gauge for the battery, and the SOH is a figure of merit of the current state of the battery, compared to its ideal conditions. Therefore, users can through the SOC, know when to charge the battery and through the SOH, know when to replace the battery.
Such an internal impedance measurement is performed by using an impedance track technology which mainly utilizes a DC impedance and an open-loop voltage to calculate an electrochemical capacity, and then looks up the SOC and SOH of battery in a look-up table according to the electrochemical capacity. However, the open-loop voltage is measured when the battery has a light load or is under a rest state, rather than when the battery is under an on-line state. Thus, the accuracy of looking up the SOC and SOH of battery in the look-up table may be poor.
Moreover, the result of battery information measurement is only updated at a specific time and can not be obtained in real time. In order to obtain the internal parameters of battery for deducing the SOC and SOH of battery in real time, it is necessary to supply an AC frequency conversion signal to the battery. Nevertheless, the AC frequency conversion signal may be make the circuit design more complicated, which leads to higher costs of production.